Tag-Archive for ◊ dowel joinery – looking inside series ◊

Finally, let’s look at the most doubtful part of the joint which is the adherence of the round dowel surface to the end grain portion of the hole.

This time, 5/16″ diameter Laurier dowels were inserted 3/4″ into holes drilled with a brad point bit in mahogany to again mimic the face grain side of the dowel joint. After drying, some of the samples were cut with an orientation to to primarily examine adhesion to the end grain portion of the hole – see the three pieces on the left in the photo below. The two pieces on the right are oriented to primarily examine adhesion to the side grain portion of the hole.

The dowels were smacked as described in the first post. The results shown are typical of several trials and they look good – the dowels adhere well to the end grain part of the hole, as seen in the first two photos below. For comparison, the next two photos show side grain and, from a separate trial, long grain adhesion.

This methodology is far from perfect. What is really demonstrated in many of the samples, essentially, is that the half joints are stronger than the half dowels. It does, nonetheless, give some sense of what is going on inside those holes with dowels glued into them. While not a joint strength test and certainly not scientific, this gives some insight into the behavior of the components of dowel joinery.

All in all, I am not surprised that in the test of the real world, the dowel joinery in my cabinets has held up well. Furthermore, these little experiments will help me proceed more knowledgeably building future projects, and I hope they will help you with your work.

Now let’s turn our attention to the face grain side of the joint where the grain of the dowels is perpendicular to that of the board. This is similar to a multiple mortise and tenon joint but among the important differences is that, because the dowel is round, there is limited side-grain-to-side-grain glue surface. So, it is reasonable to question the glue adherence of the dowel in its hole.

To mimic and investigate this part of the joint, 3/8″ diameter Laurier and Made-in-China dowels were glued 3/4″ deep into holes drilled with a brad point bit. The next day, the wood was resawn through the middle of the dowels. The dowels were then smacked to failure as described in the previous post. The orientation of this procedure primarily examines the adhesion of the dowel to the side grain portion of the hole.

As seen in the photos above, both the Laurier and the made-in-China (MiC) dowels performed well with both Titebond III and 202GF glues. The Laurier dowels were preferable in the long grain side of the joint, so they are my choice for dowel joinery, along with TB3 or 202GF glue.

Titebond No Run No Drip (TBNRND) glue did not create good adherence, and a heavy spread of it in one of the holes caused enough resistance to inserting the dowel that the wood split. It is an excellent glue for some jobs but I don’t think the best choice for this one.

Dowel joints have the same sort of cross grain dimensional change conflict as, for example, a multiple mortise and tenon. Nonetheless, I find these tests reassuring regarding the quality of the glue line in dowel joints.

Here is another reason I prefer Laurier dowels. Their spiral grooves are shallower than the straight grooves of the made-in-China (and similar) dowels, as seen in the photo below. After a 15 minute soak in water (the second photo below), which mimics the response to water based glues, the Laurier grooves expand more to take up the space in the joint. The Laurier grooves are formed by compression, and therefore will retain their expanded profile.

But wait, there’s more! The most suspect issue with a dowel is how it adheres to the end grain glue surface in its hole. That will be addressed in the next post.

In casework, doweling can be a good choice to join the end grain of one board to the face grain of another across their widths. This method for making cabinets was described and popularized by the late James Krenov in The Fine Art of Cabinetmaking. While noting that dowel joinery opens up many design options where the sides meet the top and bottom of a cabinet, Krenov warns us to use good judgement in selecting it for a piece; though durable, it is not for heavy-duty work.

The joinery in the pieces I have made with this method has remained tight for many years without a hint of problem. Nevertheless, some doubts have lingered in my mind about a joint that involves relatively little side grain gluing surface compared to the gold standards of mortise-and-tenon and dovetail joints. I wanted to see what was really going on inside dowel joints.

To do that, I had to make ’em and break ’em. My qualitative observations, combined with some intuition and educated guessing, are informative enough for my purposes. This is not a joint strength test, nor is it scientific. The photos show typical results.

First, let’s look at the “end-grain side” of the joint wherethe long grain of the dowel is parallel to the long grain of the board.

Using a DeWalt Pilot Point bit and a Krenov-style jig, 3/8″ holes were bored in poplar in the long-grain direction, deep enough to allow 3/4 inch of dowel insertion plus room for excess glue. Glue was spread only in the holes. After 24 hours, the wood was sawn through the middle of its thickness. Each half was secured in a vise, and each dowel was then hit with a hammer toward the open face to make the connection fail. The photos show the dowels snapped backwards, exposing the half hole.

3. A Laurier brand dowel, made in Canada, glued with Titebond III. Plenty of wood failure, indicating a good joint. That’s what I’m looking for.

Update Aug 29, 2017: A reader has informed me, based on information directly from Laurier, that Laurier dowels are no longer being manufactured. The owner has retired, and the machinery that makes the dowels is for sale. A few sizes remain available at justjoinery.ca

The TB No-Run No-Drip glue is very viscous, and handy in that it doesn’t run down and collect at the bottom of the hole. However, in other tests I found it did not spread well over the Laurier dowels which have less space for the glue in their spiral flutes. There was too much resistance to inserting the dowels, the glue got pushed down, and too much pressure was created. I thought it might work well with the more deeply fluted Chinese-made dowels, and they did go in easier, but TB III still made a better joint with them.

Lee Valley sells the Laurier dowels. Grizzly sells the Chinese-made dowels. To keep myself out of trouble, I emphasize that these are not scientific tests, and my conclusions that I am sharing with you are for my purposes in my shop. These should be regarded as anecdotal findings. Please refer to the manufacturers’ and vendors’ literature and make your own choices.

Of course, there is the other half of the joint to consider – the face grain board. Obviously, the same dowel must be used but it does not have to be the same glue in each half. So, in the next post, we’ll look at side grain insertion of the dowels with various options. This is the part of the joint that creates more doubt for me since much of the dowel surface is bonded to end grain surfaces inside the hole. The results of my tests surprised me.